VDMOS and IGBT are two commonly used power transistors. IGBT is comprised of BJT and MOS, which has the advantage of MOSFET's high impedance and BJT's low conduction voltage. It is very suitable for the fields of AC motor, frequency converter, switching power supply, lighting circuit, traction and driving. VDMOS is a voltage controlled device. Under the proper control of the gate voltage, the surface of the semiconductor is inversed and forms a conduction path. Thus, an appropriate amount of current flows vertically between drain and source electrodes. VDMOS has the advantages of both BJT and MOS. Compared to BJT, it switches faster and has less switching loss. Its input impedance is high and driving power is small. It has good frequency characteristics and high linear transconductance. It should be pointed out particularly that it has a negative temperature coefficient and does not have the second-breakdown problem of BJT. It has a larger safe operating area. Therefore, for both switching and linear applications, VDMOS is an ideal power device. At present, VDMOS is widely used in various fields, including motor frequency adjustment, inverter, UPS, switching power supply, electrical switch, automotive electrical and electronic ballast.
Usually, VDMOS uses a traditional integrated gate region. The channel is only formed at two sides of the gate region. In this structure, there is a large overlap between the silicon gate and the drain electrode. It has significant Qgd. In addition, the manufacture of this traditional structure is rather complex. Six (6) or seven (7) steps of masking are needed for the whole process. Therefore, the production cost is relatively higher.
In order to improve the device performance, simplify the production process and reduce the cost, the present invention provides a new structure of planar power transistor.